Prior art construction systems are known for connecting vertical structural members (e.g. 4.times.4 lumber) to one or more horizontal structural members (e.g. 2.times.4 inch lumber, etc.).
For example, U.S. Pat. No. 760,511 (Alschuler et al), discloses a square collar comprising angle-steel members and cross pieces, in which upper and lower horizontal flanges of the angle-steel members form corner pieces adapted to receive horizontal structural members.
U.S. Pat. No. 4,885,883 (Wright) teaches a unitary construction of rectangular sleeve adapted to receive a vertically aligned piece of lumber as well as horizontal sleeves for receiving horizontal structural members.
U.S. Pat. No. 4,673,308 (Reilly) teaches a corner joint having pivotal support means. The corner joint consists of a block and at least one flange extending from one surface of the block. An aperture is cut through the flange such that when the hinge mechanism is assembled, the flange is inserted into the slot which is formed by a pair of arms until the aperture is aligned with further apertures in the pair of arms. A split pin is then inserted through the three apertures to secure the components together in pivotal relationship.
Accordingly, prior art systems disclose the general concept of a construction unit comprising a generally square sleeve or collar adapted to fit over a vertical structural member, and one or more upper and lower tongues, at least one of which is adapted to pivot, for receiving horizontal structural members.